Silica gel lasts indefinitely in terms of its ability to adsorb and desorb moisture and never has to be replaced. It is the moisture within the silica gel that gets used up when it is buffering against changes in RH within an exhibit case. There are a number of methods for reconditioning silica gel. Some methods require the removal of some or all of the silica gel, and other methods allow for reconditioning silica gel within the case through the addition of a controlled amount of water or additional dry silica gel. Please refer to our PDF sheet on Reconditioning Silica Gel.